1. Field of the Invention
This invention relates to epoxidation of unsaturated (meth)acrylate esters.
2. Description of the Prior Art
(Meth)acrylate monomers which have epoxide functional groups are widely used in industry as chemical intermediates for synthetic materials. Traditionally, these monomers are being produced from epichlorohydrin via coupling with corresponding salts. Epoxidation of unsaturated organic substrates without (meth)acrylate functional groups is much easier due to the lack of (meth)acrylate functional group polymerization initiated by peroxide or radicals generated in situ. U.S. Pat. Nos. 2,833,787 and 2,833,788 describe the epoxidation of nonconjugated ethylenic compounds by hydrogen peroxide and water soluble sodium pertungstate at a PH of between 3 and 7. Similarly, unsaturated acids were epoxidized by hydrogen peroxide and sodium tungstate (J. Org. Chem., vol. 24, 54).
Olefin epoxidation using hydrogen peroxide and a water soluble alkali metal tungstate in the presence of a phase transfer agent was reported (J. Org. Chem., vol. 48, 3831 and J. Org. Chem., vol. 50, 2688). Similarly, water soluble molybdophosphoric and tungstophosphoric acid (hetero polyacids) were used in the catalytic epoxidation of olefins using hydrogen peroxide (J. Org. Chem., vol. 52, 1868 and vol. 53,3587).
The epoxidation of unsaturated (meth)acrylate esters using peracetic acid was described in U.S. Pat. No. 3,459,775 in very low yield. U.S. Pat. No. 5,283,360 describes the selective epoxidation of unsaturated (meth)acrylates using hydrogen peroxide in the presence of water soluble alkali metal molybdates and tungstates as well as heteropolyacid for cyclic substrates and phase transfer agent. According to U.S. Pat. No. 5,283,360, conversion was less than 100% and residual allylic compound.
U.S. Pat. Nos. 5,783,360 and 5,510,516 to Caubere, et al, shows epoxidation of unsaturated (meth)acrylate esters with hydrogen peroxide using a catalyst system which comprises alkali metal salts of tungstic or molybdic acids and a heteropolyacid. Caubere et al do not show (meth)acrylates which have been alkoxylated, nor do they show phosphoric acid.
GB application 2 055821A by Venturello, et al, shows epoxidation of olefins with hydrogen peroxide using a catalyst system consisting of W, Mo, or V, and at least one derivative of P or As. This application does not show epoxidation of (meth)acrylates or alkoxylated compounds.
One of the problems of the prior art processes is low catalyst lifetime and low catalytic conversion. Low conversion results in contamination with the starting material which causes crosslinking during free radical polymerization. Prior art catalytic systems include water soluble alkali metal salts of molybdates and tungstates as well as their heteropolyacids. In the presence of phase transfer agent the conversion is low and residual unsaturated (meth)acrylate remains in the initial product mixture, resulting in low stability and crosslinking in some applications. Prior art in the field requires water soluble alkali metal salts of molybdate and tungstates and their heteropolyacids.